For low pin count package products, the internal parameter setting is a tough topic. Multi-function pin is famous to adopt to solve this issue, especially for eight pin single buck pulse width modulation (PWM) controller and even package with pin count less then eight. For example, FIG. 1 is the pin configuration of Richtek Technology Corporation's product no. RT8015 whose internal circuit is shown in FIG. 2, in which a power IC 10 has eight pins that all have been occupied by specific functions and thus there is no pin available for parameter setting to the internal compensation circuit 12 from external. In consequence, the power IC 10 is limited in applications. FIG. 3 is the pin configuration of uPI Semiconductor Corporation's product no. uP6103, in which a power IC 20 also has eight pins without any vacant one for customers to set the parameter of the internal compensation circuit from external.
Therefore, it is desired a circuit and method to combine input, output or input/output with internal parameter setting at a same pin of an IC.